Automated guidance over a wire-guide path has been used in the guidance of a driverless automatically controlled vehicle (AGV) along a desired course have been set forth in U.S. Pat. Nos. 3,009,525 and 3,147,817 issued to Robert DeLiban. In such disclosures, the AGV followed a traffic path defined by a conductor energized by source not on the vehicle.
Later U.S. Pat. Nos. 4,491,570 and 4,902,948 of this assignee describe communication systems and methods for controlling a plurality of task-performing AGV's along a network of guide wires. U.S. Pat. Nos. 4,791,570 and 4,902,948 describe a guide wire logic and communications capability which provides for infinite expansion as to the number of guide wire loops and vehicles which comprise the system; accommodates polling of vehicles of the system not at predetermined times but only upon the occurrence of certain events, causes high data transmission rates to occur over low frequency carriers using the guide wires.
Today, there are a large number of installations of AGV systems which employ guide wires. However, the cost of installing and remodeling guide wire paths has proved to be a deterrent to purchase of new systems and the expansion of older installations. Factory layout flexibility and related installation and operational cost reduction, not realized with guide-wire systems, is possible with autonomously operating AGV's. Apparatus and methods of guide-wireless control of AGV's are found in U.S. Pat. Nos. 4,908,557 and 4,847,769 and in published European Patent Application 193,985.
U.S. Pat. No. 4,908,557 issued to Masahiro Sudara discloses a control apparatus which navigates along a path defined by update magnets arranged in the floor such that a null or bipolar signal is produced in each detecting sensor of a Hall sensor array located in each AGV. An algorithm is described which calculates position of the magnet based upon treating each sensor as a point or unit of measurement and performs calculations based upon a minimum distance in units of sensor positions. The precision of measurement is statistically dependent upon the physical displacement of each of the Hall sensors and the steepness of the signal about the transition between the magnet's North and South fields. As such, the precision of measurement of a magnet's position by the method described by Masahiro Sudara is of the order of magnitude of the center-to-center spacing of the Hall sensors. This level of measurement precision produces errors in vehicle bearing estimates which markedly restricts allowable distance of separation between the update magnets in the vehicle path, significant precision being required to provide assurance the vehicle will retain sufficient bearing accuracy to acquire to stay on a planned path between widely separated magnets.
U.S. Pat. No. 4,847,769 issued to Peter J. Reeve discloses a navigation system which carries out a dead reckoning calculation of the vehicles position based upon inputs from linear and angular measurements from a steering wheel and a bearing and/or a range to a target. The bearing and/or range to the target, determined by laser bearing finding equipment, provides updating data which are used to recalibrate to periodically reduce errors due to drift and other factors in the heading angle and spatial position of the AGV, angular drift in the steering angle, crabbing angle, and variations in the measured radius of the steering wheel. A Kalman filter is used to calculate corrective calibrations which are derived from the bearing and/or range to the target measurements. The laser bearing finding equipment comprises a laser emitter located at an obstruction free position on the AGV such that the vehicle may confirm its position by seeking a number of targets distributed about the AGV in a factory frame of reference.
European Patent Application 193,985 describes a grid-wireless system for navigating a free ranging vehicle. The system employs a grid of marker elements which are closely spaced to eliminate the measurement problems encountered with prior known navigation systems.
However, none of the related art addresses problems related to compatibility with existing guide-wire systems, providing the capability to operate along an existing guide-wire path and in an autonomous mode as well. Further, problems related to minimizing the numbers of floor markers required and, therefore, long distance autonomous operation between floor markers and providing unrestricted top loading surfaces for vehicles have likewise not been addressed in the known related art.